Domestic treatment of OSA and other SDB is usually done using a device that provides CPAP, e.g., nasal CPAP. A common configuration of a treatment system comprises a CPAP device and a patient interface, e.g., a nasal mask. The nasal mask forms a sealing interface with the patient's nasal passages in use so that the supply of air at positive pressure from the CPAP device may be delivered to the patient's airways. In this way, while the patient is wearing a nasal mask, their mouth is uncovered.
In some situations, patients “mouth breath” during sleep. When this happens while wearing only a nasal mask, air can pass in the mask and straight out the patient's mouth. This can lead to drying of the patient's airway and patient discomfort. This patient discomfort can to some extent be alleviated by the use of a humidifier placed between the CPAP device and the patient interface.
Many humidifiers are available, although the most convenient form is one that is either integrated with or configured to be coupled to the relevant CPAP device. While passive humidifiers can provide some relief, generally a heated humidifier is required to provide sufficient moisture to the air so that patients will be comfortable. Humidifiers typically comprise a water tub having a capacity of several hundred milliliters, a heating element, a control to enable the level of humidification to be varied, an air inlet to receive air from the blower, and an air outlet adapted to be connected to an air delivery conduit so that the humidified pressurized air may be passed to the patient interface. Usually, the water tub is removable from the system so that it can be refilled when necessary.
In making a humidification tub removable, there are two problems that need to be overcome. Firstly, there is a need for an air seal between the air outlet of the flow generator and the air inlet of the humidifier tub. An air seal is important to reduce air leaks that may result in an increased pressure drop between the air pressure generated by the flow generator and the air pressure delivered to the patient at the patient interface. Secondly, for efficient humidification, there must be adequate thermal contact between the humidification tub and the heating element.
Commonly, humidifier tubs are attached either directly to a humidifier control base or to a system base or cradle that facilitates the correct assembly of the flow generator with the humidifier. Generally, the humidifier control base or the system base or cradle comprises a heating plate that contacts the base of the humidifier tub to facilitate heating of the water within the humidifier tub. Commonly, these base systems comprise a spring loaded heater plate on to which the humidifier tub is attached. The spring loaded heater plate ensures good thermal contact with the base of the humidifier tub. For example, the Fisher & Paykel HC200 system and the Respironics RemStar heated humidifier have spring loaded heater plates. However, such spring loaded heater plates can provide a friction force against insertion of the humidifier tub, which may make installation of the humidifier tub difficult for some users, especially older or frail users.